TheCodeBreakers
code. The system appeared in four series: 5-digit codes for strategic
messages, 4-digit for high-level tactical communications, perhaps of the
rank of army headquarters, 3-digit for medium-level tactical, as of
brigade rank, and 2-digit for the front. The Soviets replaced their tactical
codes frequently, although sometimes a code that had been used in one
sector of their thousand-mile front reappeared later in another. The 4-
digit codes were en-
ciphered by 10 X 10 tables, one table for the first 2 digits and another
for the second pair. The 5-digit codes were enciphered by additive tables
of 300 groups changed daily. The Army and Navy shared the 5-digit
strategic system; border patrol and N.K.V.D. units had their own
systems, usually 4-digit. In addition, the Soviets got some Hagelin M-
209s in Lend Lease, which they apparently used as models for their own
constructions, though it is not known where these were used.
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